Difference between revisions of "West Lothian Oil Shale Formation"
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West Lothian Oil-Shale Formation is part of the Strathclyde Group in the Lothians.
The formation name was established by Chisholm et al. (1989).
The West Lothian Oil-Shale Formation is characterised by seams of oil shale in a cyclical sequence predominantly of pale coloured sandstones interbedded with grey siltstones and mudstones. Subordinate lithologies are coal, ostracod-rich limestone/dolostone, sideritic ironstone and marine beds, including bioclastic limestones with rich and relatively diverse faunas. Thick pale green-grey or grey argillaceous beds supposedly containing derived volcanic-detrital calcareous mudstone are present.
The environment of deposition was similar to that of the Aberlady Formation, but with oil shales formed in large freshwater lakes, rich in algae and other organic matter.
The type area is West Lothian, where a composite section of the formation has been built up from numerous boreholes drilled to prove the oil-shale seams. The base is well exposed in the Water of Leith near Redhall in Edinburgh (see Chisholm and Brand, 1994, p. 100, localities 1–4; Browne et al., 1999, fig. 2, col. 9). Most parts of the formation are partly exposed on the coast from South Queensferry to Blackness (NT 13 78 to 05 80).
Lower and upper boundaries
The base of the formation is taken at the base of the Humbie Marine Band, the local equivalent of the lowest Macgregor Marine Band and is underlain by the predominantly sandstone, mudstone and siltstone of the Gullane Formation (Figure 6, Column 4D). The formation is laterally equivalent to the Aberlady Formation to the east, and to the Kinghorn Volcanic Formation to the north. It is also laterally equivalent to part of the Bathgate Hills Volcanic Formation to the west.
The top of the formation is drawn at the base of the Hurlet Limestone, located at the base of the Lower Limestone Formation (Clackmannan Group).
The maximum thickness of the formation is in excess of 1120 m in West Lothian (see Browne et al., 1999; Chisholm et al., 1989, section 4.5).
Distribution and regional correlation
Age and biostratigraphical characterisation
Visean (Asbian to Brigantian). Miospores of the TC, NM and VF zones of Neves et al. (1973) are represented. The Macgregor Marine bands at the base of the formation have rich and distinctive faunas including Punctospirifer scabricosta, Pteronites angustatus and Streblopteria redesdalensis. Wilson (1952) described the B Zone ammonoid Beyrichoceratoides redesdalensis from the Cove Lower Marine Band, but this bed cannot be correlated with certainty with the Humbie Marine Band at the base of the Gullane Formation. The Granton ‘shrimp-bed’ within the formation on the shore north of Edinburgh is the locality where the soft structures of a conodont animal were first described (Briggs et al., 1983).